Systems of the type described above are generally known in commercial vehicles. The compressed air sources normally connected to the supply pressure line, which supply one or preferably (for safety reasons) a plurality of brake circuits, are used in a known way to also supply brake pressure to the braked trailer to be coupled to the commercial vehicle.
For controlling the braking processes of the trailer, it is known to provide trailer control valves (ASTV) on the commercial vehicle for transferring the brake pressure. Corresponding brake pressure lines of the trailer are connected to these trailer control valves in order to transfer brake pressure specifically to the trailer.
It is further known from the prior art to provide an electronic interface, by means of which control signals are transferred to the trailer in order to carry out specific braking processes there and to activate brake valves provided on the trailer. These brake valves can for example be ABS valves in the case of electronic brake control.
An electronic control unit that is provided on the commercial vehicle carries out the communications with the trailer in the aforementioned brake system. The electronic control unit of the commercial vehicle usually also controls the electronic brake regulation on the commercial vehicle itself. In order to initiate braking processes in all normal driving situations in which no electronic brake control is involved, the aforementioned brake systems comprise one or a plurality of control pressure lines, by means of which a control pressure is controlled by a brake pedal unit or other control means according to the driver demand and is transferred for example to the brake system of the commercial vehicle. With the brake system of the aforementioned type, such a controlled brake pressure is fed to the trailer control valve by means of the control pressure line in order to make this control pressure available to the brake system of the trailer of the commercial vehicle.
Brake systems of the aforementioned type, as used for example by the present applicant, operate reliably and satisfactorily in practice. However, there is nevertheless a need for further improvement. In particular, with the provision of compressed air for the trailer of the commercial vehicle, and hence the trailer control valve, a number of valve arrangements is necessary for implementing all the required functions, each of which comprises suitable connections and must be mounted separately. All these valves contribute in the totality thereof to a certain cost of assembly and constitute a known risk regarding a compressed air leak. In addition, the valve arrangement produces some unwanted noise during operation owing to the switching process on the one hand and owing to escaping compressed air during venting processes on the other hand, the attenuation of which can be expensive.